Question: Which of these numbers is composite? ${17,\ 27,\ 29,\ 31,\ 71}$
Explanation: A composite number is a number that has more than two factors (including 1 and itself). 17, 29, 31, and 71 each have only two factors. The factors of 27 are 1, 3, 9, and 27. Thus, 27 is the composite number.